Health of electromechanical systems and specifically of solenoid valves is a primary concern of the Space Shuttle program. The potential of delaying scheduled launch of vehicles and/or personnel injury due to failure of electromechanical systems requires the program to continuously disassemble, inspect and test Ground Support Equipment valves and flight systems valves to assure their readiness. Furthermore, disassembly inspection and testing of these systems pose an additional potential risk of hardware failure.
Flow Control Valves (FCV) are part of a flight system which requires extensive monitoring and testing. At the present time, ground systems using current measuring techniques are utilized to perform these tests. Performances of these tests have to be scheduled during the Space Shuttle processing operations. They are a one-time monitoring process, not a continuous process.
There is a need to incorporate monitoring devices in flight systems to be able to continuously monitor the health and performance of these valves during real operating conditions. It is very advantageous to the program to detect degradation and/or potential problems before they happen. This will not only provide a safer operation but will save funding spent on unnecessary inspections.
Solenoid valve status indicators are often based upon microswitches that work by physically contacting a valve's poppet assembly. Movement of the poppet serves to move the microswitch. This movement, in turn, physically opens and closes the electrical switch that is connected to a remote monitoring system that functions to indicate the valve status. All of the physical contact and movement tends to be very unreliable and is subject to wear and tear of the assemblies, friction, breakage of the switch, and even leakage of the fluid (gas or liquid) in the valve. Historically, the performance of the microswitches is so poor and costly that many solenoid valve systems elect to forgo monitoring performance of the valve. Instead, these systems rely on costly maintenance service to check and periodically replace the microswitches/valves.
U.S. Pat. No. 6,326,898 issued Dec. 4, 2001 describes a solenoid plunger position detection algorithm that allows a technician to determine if a plunger of a solenoid completes a pre-determined travel length. A measured transition time of the solenoid (monitoring the actuation current) is compared to a predetermined data or average of several solenoids. The slope of current versus time is used to identify the initial and final times of the transition. As such, U.S. Pat. No. 6,326,898 provides an indication of performance against average values, but does not provide an indication of the health of a solenoid.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art to accurately monitor the current health and predict the potential failure of solenoids.